Layer electrode for electro-chemical components and electrochemical double layer capacitor having said layer electrode

ABSTRACT

The invention concerns a layer electrode ( 6 ) for electrochemical components with a plurality of fibers ( 1 ) that all run in parallel with one another in a preferred direction at least in sections, in that the fibers ( 1 ) are connected with one another via bonding. The bonding of the fibers ( 1 ) can be produced via piercing the layer electrodes ( 6 ) with harpoons or also via sewing. The inventive layer electrodes ( 6 ) have the advantage that they can be produced thin and cost-effectively.  
     Furthermore, the invention specifies a capacitor with the inventive layer electrode ( 6 ).

[0001] The invention concerns a layer electrode for electrochemical components with a plurality of fibers. Moreover, the invention concerns a capacitor with the layer electrode.

[0002] Electrochemical double-layer capacitors are known from the printer specification EP 0 786 142 E1 whose electrodes are activated carbon fabrics. The known fabrics comprise threads woven crosswise with one another. The weaving of the fabrics is an expensive process, whereby these fabrics are elaborate with regard to the production.

[0003] Moreover, the known carbon fabrics have the disadvantage that they exhibit a relatively large thickness between 250 μm and 600 μm. Given fixed capacitor volume, only a small number of electrode layers can be introduced into the capacitor volume. With this number of the electrode layers, surface available for the contacting of the carbon cloths to the Al charge eliminators is slight, because of which the known capacitors exhibit a relatively high ohmic resistance.

[0004] Furthermore, the production of the cloths from thread interwoven together has the disadvantage that the density of carbon is relatively low due to the voids ensuing in the interweaving, whereby the volume-related capacity of a capacitor produced from the cloths is relatively low.

[0005] It is therefore the goal of the present invention to specify layer electrodes for electrochemical components that exhibit a small layer thickness and can be cost-effectively produced.

[0006] This goal is inventively achieved by a layer electrode according to patent claim 1.

[0007] Advantageous embodiments of the invention, as well as a capacitor with the inventive layer electrode, are to be learned from the further claims.

[0008] The invention specifies a layer electrode for electrochemical components that comprise a plurality of fibers that all run at least in sections in parallel in a preferred direction, and in which the fibers are connected with one another via bonding.

[0009] The inventive layer electrode has the advantage that, due to the fibers running in parallel in a single preferred direction, the interweave of fibers or threads can be abandoned. The inventive layer electrode can thereby be cost-effectively produced. Moreover, since the fibers are connected with one another via bonding, the superimposition and interweaving with one another of the fibers to produce the cohesion of the elements of the layer electrode is no longer necessary, whereby it is possible to realize substantially smaller layer thicknesses for the layer electrode, namely layer thicknesses between 10 and 500 μm.

[0010] In particular, the fibers can be activated carbon fibers that exist as lines (also known in English as “tow”).

[0011] With decreasing layer thickness, the number of layer electrodes that can be introduced into a capacitor in a predetermined capacitor volume increases. Since the area of the layer electrode available for contacting is predetermined by the area of the layer thickness, and since the entirety of the contact resistances for a capacitor can be represented by a parallel circuiting of individual contact resistances that respectively represent individual layer electrode [sic], the contact resistance, and with it the ohmic loss of a capacitor, decreases with increasing number of layer electrodes.

[0012] The bonding of the fibers among one another can, for example, be generated in that a line of fibers is pierced by needles with barbs transverse to the fiber direction. After removing such needles, some fiber sections run variant to the preferred direction and are interlocked with one another. The mechanical cohesion within the layer electrode is thereby produced. However, the proportion of the fibers comprising fiber sections variant to the preferred direction is maximally 20%, such that the fiber line clearly differentiates itself from a non-woven material where the individual fibers exhibit no preferred direction at all.

[0013] In a further exemplary embodiment of the invention, a number of fibers can be stranded with one another and thus form a thread. This exemplary embodiment of the invention has the advantage that the mechanical cohesion transverse to the preferred direction is improved in comparison to the non-stranded fibers.

[0014] Furthermore, the inventive embodiment of the layer electrode has the advantage that it enables an increased material density in comparison to fibers interwoven with one another, whereby electrochemical double-layer capacitors produced with the layer electrode an exhibit an increased capacity.

[0015] In fibers stranded with one another into a thread, the bonding of the threads, and therefore the fibers forming the threads, can also be realized among themselves via fiber sections that are interlocked with one another running variant to the preferred direction.

[0016] A further possibility to produce the mechanical cohesion of the layer electrode is to sew up the fibers with one another transverse to the fiber direction by means of a sewing thread. Synthetics, that are converted into carbon fibers via pyrolysis (also known as carbonization) as well as subsequent activation of the surface, are preferably used as fibers. The sewing up of the fibers with a sewing thread can either ensue before the pyrolysis and the activation of the synthetic raw material or, however, also first after the activation. As materials for the sewing thread, all materials are suitable that do not degrade the electrical properties of the electrochemical component. For the case that the electrochemical component is an electrochemical double-layer capacitor, for example polypropylene, polyethylene, or also Teflon are to be considered as sewing threads.

[0017] In order to not unnecessarily increase the layer thickness of the layer electrode, sewing threads with a thickness between 10 μm and 50 μm are preferably used. The sewing threads can comprise an individual fiber or also a thread.

[0018] In a further embodiment of the invention, the cohesion of the fibers within the layer electrode can also be imparted in that a material acting as the bonding between the fibers is applied in places on the surface of the layer electrode. The material imparting the bonding between the fibers can likewise be introduced in places into the layer electrode.

[0019] All materials are suitable for this that do not degrade the electrical properties of the electrochemical component. In the case of an electrochemical double-layer capacitor, in particular materials are suitable that are inert with regard to the electrolytes uses in electrochemical double-layer capacitors. To stabilize the layer electrode, therefore considered are, for example, carbon as a material placed or, respectively, deposited in the layer electrode or on its surface by means of chemical vapor deposition. However, by means of chemical vapor deposition, further materials (in particular metals such as, for example, aluminum or copper) can also be brought [sic] on or in the layer electrode.

[0020] Furthermore, the cohesion of the fibers in the layer electrode is generated or, respectively, produced via polymer additives. Possible polymer additives are, for example, polyethylene, polypropylene, polyvinylfluoride, and tetrafluoropolyethylene. The polymer additivesa are preferably supplemented with a weight proportion between 2 and 20% dependent on the carbon content of the layer electrode.

[0021] The use of a metal as the material imparting bonding between the fibers has the advantage that it can simultaneously be used for contacting the layer electrode.

[0022] Metal, such as for example aluminum or copper, can also be brought on or in the electrode via flame spraying, arc spraying, or vapor deposition. Also considered is the pressing of a layer electrode into a film of softened metal that is heated with a applied heating surfaces or heating rollers via electrical heating, convection heat, radiant heat, or also induction heat or, respectively, heating. In these methods, it is advantageous to set the layer electrode or, respectively, the fibers of the layer electrode in the preferred direction under a tensile stress, such that a substantially parallel alignment of the fibers is ensured during the insertion of the fibers into the metal.

[0023] As raw material for the fibers, synthetics that comprise C₆ rings can be used with particular advantage. These synthetics can be pyrolized via heating under exclusion of air or, respectively, in an atmosphere with low oxygen content, such that they almost completely convert to carbon. This event is also known as carbonization. Subsequent to the carbonization of the fibers, the surface of the fibers can be activated via etching processes. The etching can ensue via gas treatment, for example by means of CO₂ or H₂O, as well as chemically or electrochemically. By activating the fibers, the surfaces of the fibers are greatly increased. For example, a specific surface of 3000 m²/g can be generated from a specific surface of 100 m²/g.

[0024] For example, phenol aldehyde fibers, cellulose fibers, pitch, polyvinyl alcohol and its derivatives, or also polyacrylnitrile can be used.

[0025] Furthermore, it is advantageous to use fibers with a thickness between 5 and 50 μm, since production of thin layer electrodes with a thickness between 5 and 500 μm is eased with such fibers. Given the use of very thin fibers, if necessary a plurality of fibers can also be used on top of one another in order to form the layer electrode. Given the use of a plurality of fibers one atop the other, the layer electrode resulting from this has the advantage of an increased mechanical stability. However, in contrast to this it is also possible that the layer electrode comprises a single fiber layer. The thinnest layer electrode possible given fiber strength can thereby then be produced.

[0026] Moreover, the invention specifies an electrochemical capacitor that comprises a capacitor winding with two inventive layer electrodes. The layer electrodes are impregnated with a fluid containing ions and separated from one another with a separation layer. The separation layer electrically isolates the layer electrodes from one another and is permeable for the ions of the fluid. Each of the layer electrodes is connected with a contacting layer that enables the electrical contacting of the layer electrodes over an external connection of the capacitor. The capacitor winding can thereby in particular be guided as a layer stack of electrode layer pairs one above the other. The contacting layers can comprise lugs that are led through one side of the layer stack from this and are contacted with an external connection of the capacitor.

[0027] In the following, the invention is more closely explained using exemplary embodiments and the figures appertaining thereto.

[0028]FIG. 1 shows, for example, an inventive layer electrode in perspective view

[0029]FIG. 2 shows, for example, a first embodiment of the mechanical stabilization of a layer electrode in a schematic cross section.

[0030]FIG. 3 shows, for example, a further embodiment of the mechanical stabilization of a layer electrode in a schematic cross section.

[0031]FIG. 4 shows an inventive layer electrode on whose surface is applied a material imparting the bonding between the fibers, in schematic cross section.

[0032]FIG. 5 shows, for example, a capacitor winding of a capacitor in schematic cross section.

[0033]FIG. 1 shows an inventive layer electrode with fibers 1 running in a preferred direction. The preferred direction is indicated with the arrow. Each fiber 1 is thereby arranged in direct contact with an adjacent fiber 1, which is particularly advantageous for the material density.

[0034]FIG. 2 shows the cohesion between fibers 1 as it is produced via fiber sections 2 running variant to the preferred direction (indicated by an arrow) that are interlocking. The fibers 1 are thereby stranded into a thread 5.

[0035]FIG. 3 shows fibers 1 of a thickness D that are adjacent in a single layer and are sewn up with one another by a sewing thread 3. The sewing thread 3 can be substantially thinner than the fibers 1, whereby no significant increase in the layer thickness results for the layer electrode due to the sewing up of the fibers 1. It is to be noted that the separation between the fibers is shown enlarged for the purpose of the of the explanation of the sewing up.

[0036]FIG. 4 shows a layer electrode 6 that is produced from a line of adjacent fibers 1 according to FIG. 1 via sporadic vapor deposition of an aluminum metal on the surface, which forms a material 4 that imparts the bonding between the fibers 1. The vapor deposition may only ensue in places since otherwise the fibers would exhibit a too-small free (and therewith active) surface. The layer thickness d of the layer electrode 6 is 50 μm in the example according to FIG. 4. Fibers 1 with a thickness of 10 μm were thereby used.

[0037]FIG. 5 shows the part of a layer winding of an electrochemical double-layer capacitor with layer electrodes 6 that are separated from one another by a separation layer 7. The layer electrodes 6 are impregnated with an electrolyte. The isolated separation layer 7 is permeable for the ions of the electrolyte containing ions. The electrode layers 6 can be laterally electrically contacted by means of the contacting layer 8, in particular by means of the contact lugs 9 of which protruding from the layer electrodes 6.

[0038] The invention is not limited to the shown exemplary embodiment, but rather is defined in its general form by patent claim 1. 

1-26. cancelled.
 27. A layer electrode for electrochemical components, said electrode comprising a plurality of fibers which run in parallel with one another in a preferred direction in at least sections, said fibers being connected to one another by bonding.
 28. A layer electrode according to claim 27, which has a layer thickness between 5 μm and 500 μm.
 29. A layer electrode according to claim 27, wherein fiber sections running variant to the preferred direction are interlocked with one another.
 30. A layer electrode according to claim 27, wherein fibers are sewed with one another by a sewing thread.
 31. A layer electrode according to claim 27, wherein a material acting as a bond between fibers is introduced in places on the electrode.
 32. A layer electrode according to claim 27, wherein a plurality of fibers are stranded to one another into a thread.
 33. A layer electrode according to claim 27, wherein a material is applied in places on the surface of the layer electrode.
 34. A layer electrode according to claim 33, wherein the material is inert with regard to electrolytes used in electrochemical double-layer capacitors.
 35. A layer electrode according to claim 34, wherein the material is a metal.
 36. A layer electrode according to claim 34, wherein the material is a polymer.
 37. A layer electrode according to claim 36, wherein the material is selected from a group consisting of polyethylene, polypropylene, polyvinyldifluoride and polytetrafluorethylene.
 38. A layer electrode according to claim 34, wherein the material is elementary carbon.
 39. A layer electrode according to claim 38, wherein the material is applied via a method selected from flame spraying and arc spraying.
 40. A layer electrode according to claim 38, wherein the material is applied by vapor depositing.
 41. A layer electrode according to claim 27, wherein the fibers are produced from a synthetic that has C₆ rings.
 42. A layer electrode according to claim 41, wherein the fibers are pyrolized.
 43. A layer electrode according to claim 42, wherein the surface of the fibers is roughened via an etching process.
 44. A layer electrode according to claim 27, wherein the fibers exhibit a thickness between 5 μm and 50 μm.
 45. A capacitor with a capacitor winding, said capacitor winding comprising two layer electrodes, each layer electrode comprising a plurality of fibers running parallel with one another in a preferred direction, at least in sections, the fibers being connected with one another, said two-layer electrodes being impregnated with a fluid containing ions, a separation layer permeable to the ions of the fluid separating the two-layer electrodes from one another and each layer electrode being connected with a contacting layer. 